Fluid handling structure, a lithographic apparatus and a device manufacturing method

ABSTRACT

A fluid handling structure for a lithographic apparatus configured to contain immersion fluid to a region, the fluid handling structure having, at a boundary of a space: at least one gas knife opening in a radially outward direction of the space; and at least one gas supply opening in the radially outward direction of the at least gas knife opening relative to the space. The gas knife opening and the gas supply opening both provide substantially pure CO2 gas so as to provide a substantially pure CO2 gas environment adjacent to, and radially outward of, the space.

This application is a continuation of U.S. patent application Ser. No.16/778,635, filed on Jan. 31, 2020, now allowed, which is a continuationof U.S. patent application Ser. No. 15/537,214, filed on Jun. 16, 2017,now U.S. Pat. No. 10,551,748, which is the U.S. national phase entry ofPCT patent application no. PCT/EP2015/078842, filed on Dec. 7, 2015,which claims the benefit of priority of European patent application no.14199085.3, filed on Dec. 19, 2014, each of the foregoing applicationsis incorporated herein in its entirety by reference.

FIELD

The present description relates to a fluid handling structure, alithographic apparatus and a method for manufacturing a device using alithographic apparatus.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system PS and the substrate. In an embodiment, the liquidis distilled water, although another liquid can be used. An embodimentof the invention will be described with reference to liquid. However,another fluid may be suitable, particularly a wetting fluid, anincompressible fluid and/or a fluid with higher refractive index thanair, desirably a higher refractive index than water. Fluids excludinggases are particularly desirable. The point of this is to enable imagingof smaller features since the exposure radiation will have a shorterwavelength in the liquid. (The effect of the liquid may also be regardedas increasing the effective numerical aperture (NA) of the system andalso increasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein, or a liquid with a nano-particle suspension (e.g. particleswith a maximum dimension of up to 10 nm). The suspended particles may ormay not have a similar or the same refractive index as the liquid inwhich they are suspended. Other liquids which may be suitable include ahydrocarbon, such as an aromatic, a fluorohydrocarbon, and/or an aqueoussolution.

Submersing the substrate, or the substrate and the substrate table, in abath of liquid (see, for example, U.S. Pat. No. 4,509,852) means thatthere is a large body of liquid that must be accelerated during ascanning exposure. This requires additional or more powerful motors andturbulence in the liquid may lead to undesirable and unpredictableeffects.

In an immersion apparatus, immersion fluid is handled by an immersionsystem, device, structure or apparatus. In an embodiment the immersionsystem may supply immersion fluid and may be referred to as a fluidsupply system. In an embodiment the immersion system may at least partlyconfine immersion fluid and may be referred to as a fluid confinementsystem. In an embodiment the immersion system may provide a barrier toimmersion fluid and thereby be referred to as a barrier member, such asa fluid confinement structure. In an embodiment the immersion systemcreates or uses a flow of gas, for example to help in controlling theflow and/or the position of the immersion fluid. The flow of gas mayform a seal to confine the immersion fluid so the immersion system maycomprise a fluid handling structure, which may be referred to as a sealmember, to provide the flow of gas. In an embodiment, immersion liquidis used as the immersion fluid. In that case the immersion system may bea liquid handling system.

SUMMARY

If the immersion liquid is confined by an immersion system to alocalized area on a surface which is under the projection system, ameniscus extends between the immersion system and the surface. If themeniscus collides with a droplet on the surface, this may result ininclusion of a bubble in the immersion liquid. The droplet may bepresent on the surface for various reasons, for example, due to aleakage from the immersion system. A bubble in the immersion liquid canlead to imaging errors, for example by interfering with a projectionbeam during imaging of the substrate.

It is desirable, for example, to provide a lithographic apparatus inwhich the likelihood of bubble inclusion is at least reduced.

In an embodiment, there is provided an immersion system comprising afluid handling structure configured to contain immersion fluid to aregion external to the fluid handling structure, the fluid handlingstructure having, at a boundary of a space: at least one gas knifeopening in a radially outward direction from the space; and at least onegas supply opening in the radially outward direction from the at leastone gas knife opening relative to the space; and the immersion systemfurther comprising a gas supply system configured to supplysubstantially pure CO₂ gas through the at least one gas knife openingand the at least one gas supply opening so as to provide an atmosphereof substantially pure CO₂ gas adjacent to, and radially outward of, thespace.

In an embodiment, there is provided a device manufacturing methodcomprising projecting a projection beam of radiation via an immersionfluid onto a substrate in a lithographic apparatus comprising animmersion system, wherein the immersion system comprises a fluidhandling structure configured to contain the immersion fluid to a regionexternal to the fluid handling structure, the fluid handling structurehaving, at a boundary of a space: at least one gas knife opening in aradially outward direction from the space; and at least one gas supplyopening in the radially outward direction from the at least one gasknife opening relative to the space; and the method comprising supplyingsubstantially pure CO₂ gas through the at least one gas knife openingand the at least one gas supply opening so as to provide an atmosphereof substantially pure CO₂ gas adjacent to, and radially outward of, thespace.

In an embodiment, there is provided a lithographic apparatus comprisingan immersion system comprising a fluid handling structure configured tocontain immersion fluid to a region external to the fluid handlingstructure, the fluid handling structure having, at a boundary of aspace: at least one gas knife opening in a radially outward directionfrom the space; and at least one gas supply opening in the radiallyoutward direction from the at least one gas knife opening relative tothe space; and the immersion system further comprising a gas supplysystem configured to supply substantially pure CO₂ gas the at least onegas knife opening and the at least one gas supply opening so as toprovide an atmosphere of substantially pure CO₂ gas adjacent to, andradially outward of, the space.

In an embodiment, there is provided an immersion system comprising afluid handling structure configured to contain immersion fluid to aregion, the fluid handling structure having, at a boundary of a space:at least one gas knife opening in a radially outward direction from thespace; at least one gas supply opening in the radially outward directionfrom the at least one gas knife opening relative to the space; and a gassupply system configured to supply gas through the at least one gasknife opening and the at least one gas supply opening, wherein gas exitsthe at least one gas knife opening at a higher gas velocity than gasexiting the at least one gas supply opening.

In an embodiment, there is provided a device manufacturing methodcomprising projecting a projection beam of radiation via an immersionfluid onto a substrate in a lithographic apparatus comprising animmersion system, wherein the immersion system comprises a fluidhandling structure configured to contain the immersion fluid to a regionexternal to the fluid handling structure, the fluid handling structurehaving, at a boundary of a space: at least one gas knife opening in aradially outward direction from the space; and at least one gas supplyopening in the radially outward direction from the at least one gasknife opening relative to the space; and the method comprising supplyinggas through the at least one gas knife opening and the at least one gassupply opening, wherein gas exits the at least one gas knife opening ata higher gas velocity than gas exiting the at least one gas supplyopening.

In an embodiment, there is provided a lithographic apparatus comprisingan immersion system comprising a fluid handling structure configured tocontain immersion fluid to a region external to the fluid handlingstructure, the fluid handling structure having, at a boundary of aspace: at least one gas knife opening in a radially outward directionfrom the space; and at least one gas supply opening in the radiallyoutward direction from the at least one gas knife opening relative tothe space; and the immersion system further comprising a gas supplysystem configured to supply gas through the at least one gas knifeopening and the at least one gas supply opening, wherein gas exits theat least one gas knife opening at a higher gas velocity than gas exitingthe at least one gas supply opening.

In an embodiment, there is provided a fluid handling structureconfigured to contain immersion fluid to a region, the fluid handlingstructure having, at a boundary of a space: at least one gas knifeopening in a radially outward direction from the space; and at least onegas supply opening in the radially outward direction from the at leastone gas knife opening relative to the space, wherein the at least onegas supply opening comprises a mesh.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict an immersion system for use in a lithographicprojection apparatus;

FIG. 4 depicts, in cross-section, a further immersion system for use ina lithographic projection apparatus;

FIG. 5 depicts, in plan, an immersion system for use in a lithographicprojection apparatus;

FIG. 6 depicts, in plan, an immersion system for use in a lithographicprojection apparatus;

FIG. 7 illustrates, in cross-section, the forces acting on a droplet ona surface which result in a particular contact angle;

FIG. 8 is a graph of critical scan speed versus pH of immersion liquid;

FIG. 9 depicts, in cross-section, a further immersion system for use ina lithographic projection apparatus;

FIG. 10 depicts, in cross-section an immersion system for use in alithographic apparatus;

FIG. 11 depicts, in cross-section an immersion system for use in alithographic apparatus;

FIG. 12 depicts, in cross-section an immersion system for use in alithographic apparatus; and

FIG. 13 depicts, in cross-section an immersion system for use in alithographic apparatus.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to anembodiment of the invention. The lithographic apparatus comprises:

-   -   an illuminator (otherwise referred to as an illumination system)        IL configured to condition a projection beam B, the projection        beam B being a radiation beam (e.g. UV radiation, DUV radiation        or any other suitable radiation);    -   a support structure (e.g. a mask support structure/mask table)        MT constructed to support a patterning device (e.g. a mask) MA        and connected to a first positioner PM configured to accurately        position the patterning device MA in accordance with certain        parameters;    -   a support table, e.g. a sensor table to support one or more        sensors, and/or a substrate table (e.g. a wafer table) WT or        “substrate support” constructed to hold a substrate (e.g. a        resist-coated substrate) W connected to a second positioning        device PW configured to accurately position the substrate W in        accordance with certain parameters; and    -   a projection system (e.g. a refractive projection lens system)        PS configured to project a pattern imparted to the projection        beam B by patterning device MA onto a target portion C (e.g.        comprising one or more dies) of the substrate W.

The illuminator IL may include various types of optical components, suchas refractive, reflective, magnetic, electromagnetic, electrostatic orother types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure MT supports, i.e. bears the weight of, thepatterning device MA. The support structure MT holds the patterningdevice MA in a manner that depends on the orientation of the patterningdevice MA, the design of the lithographic apparatus, and otherconditions, such as for example whether or not the patterning device MAis held in a vacuum environment. The support structure MT can usemechanical, vacuum, electrostatic or other clamping techniques to holdthe patterning device MA. The support structure MT may be a frame or atable, for example, which may be fixed or movable as required. Thesupport structure MT may ensure that the patterning device MA is at adesired position, for example with respect to the projection system PS.Any use of the terms “reticle” or “mask” herein may be consideredsynonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a projection beamB with a pattern in its cross-section such as to create a pattern in atarget portion C of the substrate W. It should be noted that the patternimparted to the projection beam B may not exactly correspond to thedesired pattern in the target portion C of the substrate W, for exampleif the pattern includes phase-shifting features or so called assistfeatures. Generally, the pattern imparted to the projection beam B willcorrespond to a particular functional layer in a device being created inthe target portion C, such as an integrated circuit.

The patterning device MA may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam (e.g. a projection beam B) in differentdirections. The tilted mirrors impart a pattern in a projection beam Bwhich is reflected by the mirror matrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system PS, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion liquid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the lithographic apparatus is of a transmissive type(e.g. employing a transmissive mask). Alternatively, the lithographicapparatus may be of a reflective type (e.g. employing a programmablemirror array of a type as referred to above, or employing a reflectivemask).

The lithographic apparatus may comprise a measurement table (notdepicted in FIG. 1) that is arranged to hold measurement equipment, suchas sensors to measure properties of the projection system PS. In anembodiment, the measurement table is not configured to hold a substrateW. The lithographic apparatus may be of a type having two (dual stage)or more tables (or stage or support), e.g., two or more substrate tablesWT, or a combination of one or more substrate tables WT and one or moresensor or measurement tables. In such “multiple stage” machines themultiple tables may be used in parallel, or preparatory steps may becarried out on one or more tables while one or more other tables arebeing used for exposure. The lithographic apparatus may have two or morepatterning device tables (or stages or support), e.g. two or moresupport structures MT, which may be used in parallel in a similar mannerto substrate tables WT, sensor tables and measurement tables.

Referring to FIG. 1, the illuminator IL receives a projection beam Bfrom a source SO of radiation. The source SO and the lithographicapparatus may be separate entities, for example when the source SO is anexcimer laser. In such cases, the source SO is not considered to formpart of the lithographic apparatus and the projection beam B is passedfrom the source SO to the illuminator IL with the aid of a beam deliverysystem BD comprising, for example, suitable directing mirrors and/or abeam expander. In other cases the source SO may be an integral part ofthe lithographic apparatus, for example when the source SO is a mercurylamp. The source SO and the illuminator IL, together with the beamdelivery system BD if required, may be referred to as a radiationsystem.

The illuminator IL may comprise an adjuster AD configured to adjust theangular intensity distribution of the projection beam B. Generally, atleast the outer and/or inner radial extent (commonly referred to asσ-outer and σ-inner, respectively) of the intensity distribution in apupil plane of the illuminator IL can be adjusted. In addition, theilluminator IL may comprise various other components, such as anintegrator IN and a condenser CO. The illuminator IL may be used tocondition the projection beam B, to have a desired uniformity andintensity distribution in its cross-section. Similar to the source SO,the illuminator IL may or may not be considered to form part of thelithographic apparatus. For example, the illuminator IL may be anintegral part of the lithographic apparatus or may be a separate entityfrom the lithographic apparatus. In the latter case, the lithographicapparatus may be configured to allow the illuminator IL to be mountedthereon. Optionally, the illuminator IL is detachable and may beseparately provided (for example, by the lithographic apparatusmanufacturer or another supplier).

The projection beam B is incident on the patterning device (e.g., mask)MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device MA. Having traversed the patterningdevice MA, the projection beam B passes through the projection systemPS, which focuses the projection beam B onto a target portion C of thesubstrate W. With the aid of the second positioning device PW and aposition sensor IF (e.g. an interferometric device, linear encoder orcapacitive sensor), the substrate table WT can be moved accurately, e.g.so as to position different target portions C in the path of theprojection beam B. Similarly, the first positioning device PM andanother position sensor (which is not explicitly depicted in FIG. 1) canbe used to accurately position the patterning device MA with respect tothe path of the projection beam B, e.g. after mechanical retrieval froma mask library, or during a scan.

In general, movement of the support structure MT may be realized withthe aid of a long-stroke module (coarse positioning) and a short-strokemodule (fine positioning), which both form part of the first positioningdevice PM. Similarly, movement of the substrate table WT may be realizedusing a long-stroke module and a short-stroke module, which both formpart of the second positioning device PW. The long-stroke module isarranged to move the short-stroke module over a long range with limitedprecision. The short-stroke module is arranged to move the supportstructure MT and/or substrate table WT over a short range relative tothe long-stroke module with high precision. In the case of a stepper (asopposed to a scanner) the support structure MT may be connected to ashort-stroke actuator only, or may be fixed.

Patterning device MA and substrate W may be aligned using mask alignmentmarks M1, M2 and substrate alignment marks P1, P2. Although thesubstrate alignment marks P1, P2 as illustrated occupy dedicated targetportions, they may be located in spaces between target portions C. Markslocated in spaces between the target portions C are known as scribe-lanealignment marks). Similarly, in situations in which more than one die isprovided on the patterning device MA, the mask alignment marks M1, M2may be located between the dies.

The depicted lithographic apparatus may be used to expose a substrate Win at least one of the following modes of use:

1. In step mode, the support structure MT and the substrate table WT arekept essentially stationary, while an entire pattern imparted to theprojection beam B is projected onto a target portion C at one time (i.e.a single static exposure). The substrate table WT is then shifted in theX direction and/or Y direction (i.e. a stepping direction) so that adifferent target portion C can be exposed. In step mode, the maximumsize of the exposure field limits the size of the target portion Cimaged in a single static exposure.

2. In scan mode, the support structure MT and the substrate table WT arescanned synchronously while a pattern imparted to the projection beam Bis projected onto a target portion C (i.e. a single dynamic exposure).The velocity and direction of the substrate table WT relative to thesupport structure MT may be determined by the (de-)magnification andimage reversal characteristics of the projection system PS. In scanmode, the maximum size of the exposure field limits the width (in anon-scanning direction) of the target portion C in a single dynamicexposure, whereas the length of the scanning motion determines theheight (in a scanning direction) of the target portion C.

3. In another mode, the support structure MT is kept essentiallystationary holding a programmable patterning device, and the substratetable WT is moved or scanned while a pattern imparted to the projectionbeam B is projected onto a target portion C. In this mode, generally apulsed radiation source is employed as the source SO and theprogrammable patterning device is updated as required after eachmovement of the substrate table WT or in between successive radiationpulses during a scan. This mode of operation can be readily applied tomaskless lithography that utilizes a programmable patterning device,such as a programmable mirror array of a type as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

Although specific reference may be made in this text to the use of alithographic apparatus in the manufacture of integrated circuits, itshould be understood that the lithographic apparatus described hereinmay have other applications in manufacturing components with microscale,or even nanoscale, features, such as the manufacture of integratedoptical systems, guidance and detection patterns for magnetic domainmemories, flat-panel displays, liquid-crystal displays (LCDs), thin-filmmagnetic heads, etc.

Arrangements for providing liquid between a final element of theprojection system PS and the substrate W can be classed into threegeneral categories of immersion system. These include a bath typearrangement, a localized immersion system and an all-wet immersionsystem.

In the bath type arrangement, substantially the whole of the substrate Wand optionally part of the substrate table WT is submersed in a bath ofliquid.

The localized immersion system uses a liquid supply system in whichliquid is only provided to a localized area of the substrate W. The areafilled by liquid is smaller in plan than the top surface of thesubstrate W and the area filled with liquid remains substantiallystationary relative to the projection system PS while the substrate Wmoves underneath that area. FIGS. 2-6 and 9-13 show different immersionsystems which can be used as such a liquid supply system. A meniscuscontrolling feature can be present to seal liquid to the localized area.One way which has been proposed to arrange for this is disclosed in PCTpatent application publication no. WO 99/49504. The meniscus controllingfeature may be a meniscus pinning feature.

In the all wet arrangement, the liquid is unconfined. The whole topsurface of the substrate W and all or part of the substrate table WT iscovered in immersion liquid. The depth of the liquid covering at leastthe substrate W is small. The liquid may be a film, such as a thin film,of liquid on the substrate W. Immersion liquid may be supplied to or inthe region of the projection system PS and a facing surface facing theprojection system PS (such a facing surface may be the surface of thesubstrate W and/or the substrate table WT). Any of the liquid supplydevices of FIG. 2 or FIG. 3 can also be used in such a liquid supplysystem. However, a meniscus controlling feature is not present, notactivated, not as efficient as normal or otherwise ineffective to sealliquid to only a localized area.

FIG. 2 schematically depicts an immersion system (which can otherwise bereferred to as a localized liquid supply system or fluid handlingsystem) with a fluid handling structure 12 (which could also be referredto as a liquid confinement structure), which extends along at least apart of a boundary of a space 11 between a final element of theprojection system PS and the substrate table WT or substrate W. (Pleasenote that reference in the following text to surface of the substrate Walso refers in addition or in the alternative to a surface of thesubstrate table WT, unless expressly stated otherwise.) In anembodiment, a seal is formed between the fluid handling structure 12 andthe surface of the substrate W and which may be a contactless seal suchas a gas seal 16 (such a system with a gas seal is disclosed in Europeanpatent application publication no. EP-A-1,420,298). The seal can beprovided by a meniscus controlling feature.

The fluid handling structure 12 at least partly contains liquid in thespace 11 between the final element of the projection system PS and thesubstrate W. The space 11 is at least partly formed by the fluidhandling structure 12 positioned below and surrounding the final elementof the projection system PS. Liquid is brought into the space 11 belowthe projection system PS and within the fluid handling structure 12 byopening 13. The liquid may be removed by opening 13. Whether liquid isbrought into the space 11 or removed from the space 11 by the opening 13may depend on the direction of movement of the substrate W and substratetable WT.

The liquid may be contained in the space 11 by the gas seal 16 which,during use, is formed between the bottom of the fluid handling structure12 and the surface of the substrate W. The gas in the gas seal 16 isprovided under pressure via inlet 15 to the gap between the fluidhandling structure 12 and substrate W. The gas is extracted via achannel associated with outlet 14. The overpressure on the gas inlet 15,vacuum level on the outlet 14 and geometry of the gap are arranged sothat there is a high-velocity gas flow inwardly that confines theliquid. The force of the gas on the liquid between the fluid handlingstructure 12 and the substrate W contains the liquid in the space 11.Such a system is disclosed in United States patent applicationpublication no. US 2004-0207824, which is hereby incorporated byreference in its entirety.

FIG. 3 is a side cross sectional view that depicts a further immersionsystem according to an embodiment. The arrangement illustrated in FIG. 3and described below may be applied to the lithographic apparatusdescribed above and illustrated in FIG. 1. The liquid supply system isprovided with a fluid handling structure 12, which extends along atleast a part of a boundary of a space 11 between the final element ofthe projection system PS and the substrate table WT or substrate W.(Please note that reference in the following text to surface of thesubstrate W also refers in addition or in the alternative to a surfaceof the substrate table WT, unless expressly stated otherwise.)

The fluid handling structure 12 at least partly contains liquid in thespace 11 between a final element of the projection system PS and thesubstrate W. The space 11 is at least partly formed by the fluidhandling structure 12 positioned below and surrounding the final elementof the projection system PS. In an embodiment, the fluid handlingstructure 12 comprises a main body member 53 and a porous member 83. Theporous member 83 is plate shaped and has a plurality of holes (i.e.,openings or pores). In an embodiment, the porous member 83 is a meshplate wherein numerous small holes 84 are formed in a mesh. Such asystem is disclosed in United States patent application publication no.US 2010/0045949 A1, which is hereby incorporated by reference in itsentirety.

The main body member 53 comprises supply ports 72, which are capable ofsupplying the liquid to the space 11, and a recovery port 73, which iscapable of recovering the liquid from the space 11. The supply ports 72are connected to a liquid supply apparatus 75 via passageways 74. Theliquid supply apparatus 75 is capable of supplying the liquid to thesupply ports 72. The liquid that is fed from the liquid supply apparatus75 is supplied to each of the supply ports 72 through the correspondingpassageway 74. The supply ports 72 are disposed in the vicinity of theoptical path at prescribed positions of the main body member 53 thatface the optical path. The recovery port 73 is capable of recovering theliquid from the space 11. The recovery port 73 is connected to a liquidrecovery apparatus 80 via a passageway 79. The liquid recovery apparatus80 comprises a vacuum system and is capable of recovering the liquid bysuctioning it via the recovery port 73. The liquid recovery apparatus 80recovers the liquid LQ recovered via the recovery port 23 through thepassageway 29. The porous member 83 is disposed in the recovery port 73.

In an embodiment, to form the space 11 with the liquid between theprojection system PS and the fluid handling structure 12 on one side andthe substrate W on the other side, liquid is supplied from the supplyports 72 to the space 11 and the pressure in a recovery chamber 81 inthe fluid handling structure 12 is adjusted to a negative pressure so asto recover the liquid via the holes 84 (i.e., the recovery port 73) ofthe porous member 83. Performing the liquid supply operation using thesupply ports 72 and the liquid recovery operation using the porousmember 83 forms the space 11 between the projection system PS and thefluid handling structure 12 on one side and the substrate W on the otherside.

FIG. 4 illustrates a fluid handling structure 12 which is part of animmersion system (such as a liquid supply system). The fluid handlingstructure 12 extends around the periphery (e.g. circumference) of thefinal element of the projection system PS. The fluid handling structure12 is configured to contain immersion fluid to a region. The region maybe external to the fluid handling structure 12. The region may bebetween the final element of the projection system PS and the substrateW and/or substrate table WT. The fluid handling structure 12 maycomprise at least one meniscus controlling feature to contain theimmersion fluid.

A plurality of openings 20 in the surface which in part defines thespace 11 provide liquid to the space 11. The liquid passes throughopenings 29 and 20 in side walls 28 and 22 respectively, throughrespective chambers 24 and 26 respectively, prior to entering the space11.

A seal is provided between the bottom of the fluid handling structure 12and a facing surface, e.g. a top surface of the substrate W, or a topsurface of the substrate table WT, or both. The facing surface is thesurface facing the bottom of the fluid handling structure 12. In FIG. 4a fluid handling structure 12 is configured to provide a contactlessseal and is made up of several components. Radially outwardly from theoptical axis of the projection system PS, there is provided a (optional)flow control plate 51 which extends into the space 11. The control plate51 may have an opening 55 to permit liquid to flow therethrough; theopening 55 may be beneficial if the control plate 51 is displaced in theZ direction (e.g., parallel to the optical axis of the projection systemPS). Radially outwardly of the flow control plate 51 on the bottomsurface of the fluid handling structure 12, facing (e.g., opposite) thefacing surface may be an opening 180. The opening 180 can provide liquidin a direction towards the facing surface. During imaging this may beuseful in preventing bubble formation in the immersion liquid by fillinga gap between the substrate W and substrate table WT with liquid.

Radially outwardly of the opening 180 may be an extractor assembly 70 toextract liquid from between the fluid handling structure 12 and thefacing surface. The extractor assembly 70 may operate as a single phaseor as a dual phase extractor. The extractor assembly 70 acts as ameniscus controlling feature.

Radially outwardly of the extractor assembly 70 is a gas knife. Asdepicted in FIG. 4, at least one gas knife opening 210 may be providedin a radially outward direction from the extractor assembly 70 toprovide a gas knife. The gas knife openings 210 may be substantiallyparallel to the edge of the extractor assembly 70. In an embodiment, thegas knife opening 210 may be a series of discrete apertures providedalong the edge of the extractor assembly 70. In use, the gas knifeopening 210 is connected to an overpressure and forms a gas knifesurrounding the meniscus controlling feature formed by the extractorassembly 70. The gas knife opening 210 may be adjacent to the meniscuscontrolling feature and is in a radially outward direction relative tothe space 11 in plan view. An arrangement of the extractor assembly 70and gas knife is disclosed in detail in United States patent applicationpublication no. US 2006-0158627 incorporated herein in its entirety byreference.

In an embodiment, the extractor assembly 70 is a single phase extractorwhich may comprise a liquid removal device, extractor or inlet such asthe one disclosed in United States patent application publication no. US2006-0038968, incorporated herein in its entirety by reference. In anembodiment, the meniscus controlling feature comprises a micro-sieve. Inan embodiment, the extractor assembly 70 comprises an inlet which iscovered in a porous material 111 which is used to separate liquid fromgas to enable single-liquid phase liquid extraction. The porous material111 may also be a micro-sieve. An under pressure in chamber 121 ischosen is such that the meniscuses formed in the holes of the porousmaterial 111 prevent ambient gas from being drawn into the chamber 121of the extractor assembly 70. However, when the surface of the porousmaterial 111 comes into contact with liquid there is no meniscus torestrict flow and the liquid can flow freely into the chamber 121 of theextractor assembly 70.

Although not specifically illustrated in FIG. 4, the fluid handlingstructure 12 may have an arrangement to deal with variations in thelevel of the liquid. This is so that liquid which builds up between theprojection system PS and the fluid handling structure 12 can be dealtwith and does not escape. One way of dealing with this liquid is toprovide a lyophobic (e.g., hydrophobic) coating on at least part of thefluid handling structure 12.

Another localized immersion system with a fluid handling structure 12makes use of a gas drag principle. The so-called gas drag principle hasbeen described, for example, in United States patent applicationpublication nos. US 2008-0212046, US 2009-0279060 and US 2009-0279062.In that localized immersion system the extraction holes are arranged ina shape which may desirably have a corner. The extractions holes may beused to provide a dual phase extractor. The corner may be aligned with apreferred direction of movement, such as the stepping direction or thescanning direction. This reduces the force on the meniscus between twoopenings in the surface of the fluid handing structure 12 for a givenspeed in the preferred direction compared to if the two openings werealigned perpendicular to the preferred direction. However, an embodimentof the invention may be applied to a fluid handling structure 12 whichhas any shape in plan, or has a component such as the outlets arearranged in any shape. Such a shape in a non-limiting list may includean ellipse such as a circle, a rectilinear shape such as a rectangle,e.g. a square, or a parallelogram such as a rhombus or a cornered shapewith more than four corners such as a four or more pointed star, forexample, as depicted in FIG. 5.

FIG. 5 illustrates schematically and in plan meniscus controllingfeatures of an immersion system including a fluid handling structure 12which may have outlets using the gas drag principle and to which anembodiment of the present invention may relate. The features of ameniscus controlling feature are illustrated which may, for example,replace the meniscus controlling features depicted by the gas seal 16,provided by the inlet 15 and the outlet 14 in FIG. 2, or at least theextractor assembly 70 shown in FIG. 4. The meniscus controlling featureof FIG. 5 is a form of extractor, for example a dual phase extractor.The meniscus controlling feature comprises a plurality of discreteopenings 50. Each opening 50 is illustrated as being circular, thoughthis is not necessarily the case. Indeed, the shape is not essential andone or more of the openings 50 may be one or more selected from:circular, elliptical, rectilinear (e.g. square, or rectangular),triangular, etc. and one or more openings may be elongate.

There may be no meniscus controlling features radially inwardly of theopenings 50. The meniscus is pinned between the openings 50 with dragforces induced by gas flow into the openings 50. A gas drag velocity ofgreater than about 15 m/s, desirably about 20 m/s is sufficient. Theamount of evaporation of liquid from the substrate W may be reduced,thereby reducing both splashing of liquid as well as thermalexpansion/contraction effects.

Various geometries of the bottom of the fluid handling structure arepossible. For example, any of the structures disclosed in U.S. patentapplication publication no. US 2004-0207824 or U.S. patent applicationSer. No. 61/181,158, filed on 26 May 2009, could be used in anembodiment of the present invention.

As can be seen in FIG. 5, relative to the space 11, at least one gasknife opening 210 may be provided outside the openings 50 to provide agas knife. The gas knife opening 210 may be substantially parallel tothe lines joining the openings 50 of the meniscus controlling feature.In an embodiment the gas knife opening 210 may be a series of discreteapertures provided along a side 54 of the shape. In use, the gas knifeopening 210 is connected to an over pressure and forms a gas knife(equivalent to the gas knife provided by gas knife openings 210 in FIG.4) surrounding the meniscus controlling feature formed by openings 50.The gas knife opening 210 may be adjacent to the meniscus controllingfeature and is in a radially outward direction relative to the space 11in plan view.

The gas knife in an embodiment of the invention functions to reduce thethickness of any liquid film left on a facing surface, such as thesubstrate W or substrate table WT. The gas knife helps ensure that theliquid film does not break into droplets but rather the liquid is driventowards the openings 50 and extracted. In an embodiment the gas knifeoperates to prevent the formation of a film. To achieve this, it isdesirable that the distance between the center lines of the gas knifeand of the meniscus controlling openings 50 is in the range of from 1.5mm to 4 mm, desirably from 2 mm to 3 mm. The line along which the gasknife is arranged generally follows the line of the openings 50 so thatthe distance between adjacent ones of the openings 50 and the gas knifeopening 210 is within the aforementioned ranges. Desirably the linealong which the gas knife opening 210 is arranged is parallel to theline of the openings 50. It is desirable to maintain a constantseparation between adjacent ones of the openings 50 and the gas knifeopening 210. In an embodiment this is desirable along the length of eachcenter line of the gas knife. In an embodiment the constant separationmay be in the region of one of more corners of the cornered shape.

Localized immersion systems such as those described above, withreference to FIGS. 2-5, can suffer from bubble inclusion into the space11. As can be seen, a meniscus 320 extends between the fluid handlingstructure 12 and the facing surface (e.g. the top surface of thesubstrate W) under the fluid handling structure 12. This meniscus 320illustrated in FIG. 2 and FIG. 4 defines the edge of the space 11. Whenthe meniscus 320 and a droplet collide on the surface, for example adroplet of liquid which has escaped the space 11, a bubble of gas may beincluded into the space 11. Inclusion of a bubble into the space 11 isdetrimental because a bubble of gas can lead to an imaging error.

There are certain circumstances in which it is more likely that adroplet will be left behind on the surface. For example, a droplet maybe left behind on the surface when the immersion system (andparticularly the fluid handling structure 12) is located over the edgeof a substrate W when there is relative movement between the immersionsystem/fluid handling structure 12 and the substrate W. In anotherexample, a droplet may be left behind when the immersion system (andparticularly the fluid handling structure 12) is located over a stepchange in height of the facing surface facing the fluid handlingstructure 12 and when there is relative movement between the fluidhandling structure 12 and the facing surface. In another example, adroplet may be left behind due to a relative speed between the fluidhandling structure 12 and the facing surface being too high, for examplewhen the meniscus becomes unstable, e.g. by exceeding the critical scanspeed of the facing surface. A bubble may be included into the space 11at the meniscus 400 illustrated in FIGS. 2 and 4 extending between thefluid handling structure 12 and the projection system PS. Here a bubbleof gas could be created by liquid supplied from a liquid inlet (e.g.inlet 13 in FIG. 2 and inlet 20 in FIG. 4) on a radially inward facingsurface of the fluid handling structure 12 entraining gas from betweenthe projection system PS and the fluid handling structure 12.

Ways of dealing with the difficulty of bubble inclusion haveconcentrated on improving the confinement properties of the fluidhandling structure 12. For example, the relative speed between the fluidhandling structure 12 and the facing surface has been decreased in orderto avoid spilling of liquid.

Very small bubbles of gas may dissolve in the immersion liquid beforethey reach the exposure area of the space 11. An embodiment of thepresent invention uses the fact that dissolution speed is dependent uponthe type of the trapped gas and the immersion liquid properties.

A bubble of carbon dioxide gas typically dissolves faster than a bubbleof air. A bubble of CO₂, which has a solubility fifty-five (55) timeslarger than that of nitrogen and a diffusivity of 0.86 times that ofnitrogen, will typically dissolve in a time thirty-seven (37) timesshorter than the time for a bubble of the same size of nitrogen todissolve. Supplying CO₂ adjacent to the meniscus 320 or 400 means that abubble of CO₂ gas will dissolve into the immersion liquid much fasterthan if other gases with lower diffusivity were used. Therefore, usingCO₂ in an embodiment of the present invention will reduce the number ofimaging defects thereby allowing higher throughput (e.g., higher speedof the substrate W relative to the fluid handling structure 12) andlower defectivity.

Therefore, an embodiment of the present invention may provide a gasknife which supplies substantially pure CO₂ gas to a region (e.g. to avolume, or a towards an area) adjacent to the space 11. In particular,CO₂ gas is provided such that it is present in the region adjacent tothe meniscus 320 extending between the facing surface (e.g. on substrateW or substrate table WT) and the fluid handling structure 12.

Carbon dioxide is desirable because it is readily available and may beused in immersion systems for other purposes. Carbon dioxide hassolubility in water at 20° C. and 1 atm total pressure of 1.69×10⁻³kg/kg or 37×10⁻³ mol/kg. Other gases may have one or more disadvantages,for example, other gases may react with components in the immersionlithographic apparatus and/or may be poisonous and may therefore beharder to handle and less desirable than carbon dioxide.

By using gaseous CO₂ the problem associated with the meniscus 320colliding with a droplet of liquid may be reduced. Typically a dropletof 300 micrometers would produce a bubble of 30 micrometers in diameter(i.e. a tenth the size). Such a bubble of carbon dioxide would usuallydissolve in the immersion liquid before reaching the exposure area whichmay make problems caused by a droplet less significant. Therefore, animmersion system may be more tolerant of interacting with immersionliquid which had escaped from the space 11.

Carbon dioxide gas is also provided through at least one gas supplyopening 220. The gas supply opening 220 is radially outward, i.e. in aradially outward direction in plan view relative to the space 11, of thegas knife opening 210 (and also the meniscus controlling feature, suchas the extractor 70 in FIG. 4 or the outlets 50 in FIG. 5). The at leastone gas supply opening 220 may be adjacent to the at least one gas knifeopening 210, as depicted in FIGS. 4, 5, 6, 10, 11, 12 and 13.

Providing a gas knife opening 210 for providing substantially pure CO₂gas and a gas supply opening 220 for providing substantially pure CO₂gas means that an atmosphere of substantially pure CO₂ can be providedadjacent to and radially outward of the space 11. The atmosphereadjacent to, and radial outward of, the space 11 does not containsignificant amounts of gases which do not dissolve as readily as CO₂gas.

In an embodiment of the present invention herein described, asubstantially pure CO₂ gas atmosphere is formed around the meniscus 320of immersion liquid so that any inclusion of CO₂ gas into the immersionliquid creates a gas inclusion which dissolves in the immersion liquid.In an embodiment, the atmosphere of substantially pure CO₂ gas is atleast 90% CO₂ gas. In an embodiment, the atmosphere of substantiallypure CO₂ gas is at least 95% CO₂ gas. In an embodiment, the atmosphereof substantially pure CO₂ gas is at least 99% CO₂ gas. In an embodiment,the atmosphere of substantially pure CO₂ gas is at least 99.5% CO₂ gas.In an embodiment, the atmosphere of substantially pure CO₂ gas is atleast 99.9% CO₂ gas. It is preferable that the substantially pure CO₂gas atmosphere has as high a CO₂ gas content as is achievable.

A difficulty with providing carbon dioxide gas in a lithographicapparatus is that some components, for example components of a positionmeasurement system of the substrate table WT, have impaired performancein a carbon dioxide atmosphere. In an embodiment of the presentinvention, it is ensured that a pure carbon dioxide environment ispresent near the meniscus 320 during scanning. To achieve this, it maybe necessary, for example in the embodiment of FIG. 5, to have a flowrate of carbon dioxide out of the gas knife opening 210 and the gassupply opening 220 greater than the amount of CO₂ extracted through theopenings 50. This may result in an excess of carbon dioxide leaking outfrom under the fluid handling structure 12 into the environment of themachine and particularly towards components of a position measurementsystem of the substrate table WT.

In an embodiment of the invention, in order to ensure that excess carbondioxide does not leak from under the fluid handling structure 12, atleast one gas recovery opening 61 is provided radially outward of theone or more meniscus controlling features, the gas knife opening 210 andthe gas supply opening 220 as depicted in FIG. 6. The gas recoveryopening 61 may be provided with any of the embodiments. The gas recoveryopening 61 may comprise a dual phase extractor. As an example, the dualphase extractor may have an extraction flow rate of approximately 40 to80 NI/min, however, this may vary depending on the apparatus. In thisway an environment of carbon dioxide can still be provided radiallyoutwardly of the meniscus controlling features thereby reducing bubbleinclusion to the space 11. Also, possible contamination or interruptionof functioning of components of the lithographic apparatus can bereduced or prevented.

An advantage of providing an atmosphere of substantially pure carbondioxide adjacent to the meniscus 320 is that the carbon dioxide may thendissolve in immersion liquid at the meniscus 320 under the openings 50of the meniscus controlling feature. This results in the immersionliquid at the meniscus 320 becoming slightly acidic (a decrease in pH).If the immersion liquid becomes more acidic this increases the presenceof H₃O⁺ ions. An increase in the number of H₃O⁺ ions results in thesolid-liquid surface energy (γ_(SL)) decreasing. The solid-gas surfaceenergy (γ_(SG)) does not change and neither does the liquid-gas surfaceenergy (γ_(LG)). The change in the solid-liquid surface energy thereforeaffects the equilibrium between the three surface energies. The surfacetension in the liquid meniscus, especially towards its interface withthe solid surface, is affected. The change in direction of the surfacetension as a consequence of the change in the surface energies isillustrated in FIG. 7. FIG. 7 shows the contact angle θ_(C) of thedroplet 300 on the surface 310. The relationship between the threesurface energies and the contact angle is given in the followingequation:

γ_(LG)cos θ_(C)=γ_(SG)−γ_(SL)

According to this equation a decrease in the solid-liquid electricalsurface energy (γ_(SL)) results in an increase in the contact angleθ_(C). An increase in the contact angle θ_(C) between liquid and thefacing surface, particularly at the meniscus 320, results in animprovement in performance of the meniscus controlling feature (e.g. theopenings 50). As such, a higher velocity between the fluid handlingstructure 12 and the facing surface may be achieved before liquid islost from the immersion space 11, beyond the meniscus controllingfeature.

FIG. 8 is a graph showing the pH of immersion liquid along the x axisand the critical scanning speed before liquid loss along the y axis. Thegraph is for a particular type of fluid handling structure and asubstrate W having a top coat of TCX041 available from JSR Micro, Inc.in CA, US.

FIG. 8 shows that a reduction in pH of immersion liquid leads to anincrease in critical scan speed. An increase in critical scan speedwould lead to an increase in throughput as a high scan speed can be usedwithout risk of liquid loss (which can lead to imaging errors asdescribed above). This is particularly so for larger substrates W suchas substrates with a diameter of 450 mm. This is because on such alarger substrate, relative to a smaller substrate, more scans areperformed a distance away from the edge of the substrate W, for examplein a region towards the center of the substrate W. It is the scans in aregion towards the center of the substrate W which can be performedclose to critical scan speed; whereas scans performed closer to the edgeof a substrate W may need to be performed at a slower speed than thecritical scan speed. The reason for this difference in scan speed canbe, for example, the effect of the edge of the substrate W on thestability of the meniscus 320.

Providing a gas supply opening 220 radially outwards of the gas knifeopening 210 may ensure that an atmosphere of substantially pure CO₂ gasis provided adjacent to the space 11, i.e. adjacent to the meniscus 320.If such a gas supply opening 220 was not provided, then to provide thesubstantially pure CO₂ gas atmosphere adjacent to the meniscus 320, theflow rate of the substantially pure CO₂ gas supplied by the gas knifeopening would have to be much higher, and more water marks would occurdue to the higher flow rate. For example, a gas knife opening without anadditional gas supply opening 220 may have to provide gas at a flow rateapproximately 10-20 NI/min more than the extracted gas flow rate by thedual phase extractor. If there is no gas supply opening 220 and the gasknife flow rate is kept low to avoid water marks, then bubbles thatenter the immersion liquid in the space 11 would take longer todissolve. Hence more imaging errors would occur.

However, in an embodiment of the present invention, a gas supply opening220 provides CO₂ gas radially outward of the gas knife opening 210.Therefore, if gas external to the gas knife is drawn into the atmosphereadjacent to the meniscus 320, the gas is likely to be substantially pureCO₂ gas emitted by the gas supply opening 220, such that the atmosphereadjacent to the meniscus 320 can be maintained as substantially pureCO₂. Therefore, the flow rate and/or the gas velocity, of the gas knifecan be reduced because it is not necessary to prevent gas radiallyoutward of the gas knife from entering the atmosphere adjacent to thespace 11, because the gas radially outward of the gas knife opening isalso CO₂. As such, the substantially pure CO₂ gas atmosphere can bemaintained when the gas emitted from the gas knife opening 210 is at alower flow rate.

The gas knife has a first gas velocity at which the CO₂ gas exits thegas knife opening 210. The gas supply opening 220 has a second gasvelocity at which substantially pure CO₂ gas exits the at least one gassupply opening 220. In an embodiment, the first gas velocity is greaterthan the second gas velocity. In an embodiment, the second gas velocitymay be equal to or less than approximately the dual extraction gasvelocity.

The gas knife has a first flow rate at which the CO₂ gas exits the gasknife opening 210. In an embodiment, first flow rate is less thanapproximately 30 NI/min more than the extracted gas rate by the dualphase extractor. In an embodiment, the first flow rate is preferablyless than approximately 15 NI/min more than the extracted gas rate bythe dual phase extractor. In an embodiment, the first flow rate ispreferably no more than the extracted gas flow rate by the dual phaseextractor. The gas supply opening 220 has a second flow rate at whichsubstantially pure CO₂ gas exits the at least one gas supply opening220. In an embodiment, the first flow rate is greater than the secondflow rate. In an embodiment, the second flow rate may be equal to orless than approximately the dual extraction flow rate. In an embodiment,the second flow rate is generally between 10-60 NI/min.

Generally, CO₂ gas which is provided at the atmosphere adjacent to themeniscus 320 may be humidified at high pressure. A gas knife, such asthe gas knife opening 210, provides a flow of gas which results in apressure peak on the facing surface (e.g. substrate W). The gas knifehas high stagnant pressure. Due to the high pressure change across thegas knife, i.e. a high pressure gradient, the pressure drop leads to areduction in the relative humidity of the carbon dioxide in theatmosphere adjacent to the meniscus 320. By using a gas supply opening220 in addition to the gas knife opening 210 as described above, theflow rate and/or the gas velocity, at which CO₂ gas is provided from thegas knife opening 210 is reduced (compared to when a gas substrateopening 210 is provided) and therefore, the pressure drop across the gasknife is reduced also. The flow of gas from the gas supply opening isgenerally a low impulse gas supply. Therefore, the reduction of relativehumidity of the gas across the gas knife is reduced, such that there isa lower heat load on the substrate W.

In an embodiment, the gas knife opening 210, the gas supply opening 220and, if provided, the gas recovery opening 61 are provided on the lowersurface of the fluid handling structure 12 and are at the same distancewith respect to the facing surface.

In an embodiment, the distances between each of the openings and thefacing surfaces are variable. For example, a step may be providedbetween the gas knife opening 210 and the gas supply opening 220 suchthat the gas knife opening 210 is closer to the facing surface than thegas supply opening 220 (and the gas recovery opening 61 if included).Alternatively, the gas knife opening 210 may be further away from thefacing surface than the gas supply opening 220 (and the gas recoveryopening 61, if provided). Additionally, or alternatively, a step may beprovided between the gas supply opening 220 and the gas recovery opening61 such that the gas supply opening 220 is closer to the facing surfacethan the gas recovery opening 61. Alternatively, the gas supply opening220 may be further from the facing surface than the gas recovery opening61.

In an embodiment, the distance between the openings and the facingsurface can be chosen to control the speed of the CO₂ gas on the facingsurface, i.e. an increase in distance between an opening and the facingsurface will decrease the speed of gas on the facing surface. Ingeneral, the velocity of a jet starts decreasing after a distance fromthe opening of approximately four times the diameter of the opening.This distance may be for example, approximately 150-200 micrometers. At350 micrometers the velocity of the jet, and the resulting pressure onthe facing surface, is significantly decreased. Having a high pressureat the facing surface may mean that the overall number and/or size ofdroplets radially outward of the meniscus 320 is reduced, however,resulting water marks on the substrate W may be made. Therefore, thesupply of gas through the gas supply opening 220 and the gas knifeopening 210 can be optimized in accordance with the height of theopenings above the facing surface to reduce the water marks.

The gas knife opening 210 and the gas supply opening 220 each have asurface area on the lower surface of the fluid handling structure 12.The overall surface area of the gas knife opening 210 may be smallerthan the overall surface area of the gas supply opening 220. The gasemitted from the gas knife opening 210 is at a first flow speed and thegas emitted from the gas supply opening 220 is at a second flow speed.In an embodiment, the first flow speed is greater than the second flowspeed. In an embodiment, at least one gas recovery opening 61 may beprovided radially outward of the gas supply opening 220, as depicted inFIGS. 4 and 6. However, this is not necessarily the case. For example,in the embodiment of FIG. 9 described below, the at least one gasrecovery opening 61 is provided radially inwardly of the gas supplyopening 220.

In an embodiment, the gas supply opening 220 and/or gas recovery opening61 may be provided as a single slit or as a plurality of discreteopenings.

In an embodiment, the gas recovery opening 61 at least partly surroundsthe gas supply opening 220. It may not be possible for the gas recoveryopening 61 to completely surround the gas supply opening 220. In anembodiment the gas recovery opening 61 surrounds the majority of theperimeter of the gas supply opening 220. In an embodiment the gasrecovery opening 61 may surround at least half of the perimeter. Thatsaid, in an embodiment the gas recovery opening 61 may substantiallycompletely surround the perimeter of the gas supply opening 220. A highextraction rate out of the gas recovery opening 61 (for exampleconnecting a large underpressure source to the gas recovery opening 61)at least partly mitigates for the fact that the at least one gasrecovery opening 61 does not completely surround the gas supply opening220.

In an embodiment depicted in FIG. 4, the at least one gas recoveryopening 61 is formed in the fluid handling structure 12. In oneembodiment the at least one gas recovery opening 61 is formed in anundersurface of the fluid handling structure 12. In one embodiment theat least one gas recovery opening 61 is formed in a bottom surface ofthe fluid handling structure 12. In one embodiment, the gas recoveryopening 61 is formed in the same surface in which the gas knife opening210 and the gas supply opening 220 are formed. The flow of gas out ofthe gas supply opening 220 and the gas knife opening 210 is bothradially inward towards the meniscus 320 and radially outward.

In an embodiment the radially outward flow is greater than the inwardflow. This ensures that there is minimal or no flow of gas radiallyinward from outside the fluid handling structure 12 reaching themeniscus 320. If the radially outward flow from the gas supply opening220 and the gas knife opening 210 is too low, this could have the effectof sucking in gas from the outside of the fluid handling structure 12.

The embodiments of FIG. 5 and FIG. 6 are the same as that of FIG. 4concerning the gas supply opening 220 and the gas knife opening 210. Thegas recovery opening 61, for example, as depicted in FIG. 4, FIG. 6 andFIG. 9, is not essential.

The embodiment of FIG. 9 is the same as the embodiment of FIG. 4 exceptas described below. In the embodiment of FIG. 9 the at least one gasrecovery opening 61 is radially outward of the gas knife opening 210 andradially inward of the gas supply opening 220. The gas supply opening220 is radially outward of the at least one gas recovery opening 61. Thegas knife opening 210 is radially inward of the recovery opening 61 andthe gas supply opening 220. Optionally, there may be an additional gasrecovery opening (not shown) radially outwards of the gas supply opening220. Such an additional gas recovery opening would help reduce or avoidCO₂ gas from leaking into the atmosphere around the lithographicapparatus.

Because the gas exiting the gas knife opening 210 is carbon dioxide,that gas has a higher kinetic energy than gas comprising air at the samevelocity. This is because the density of carbon dioxide is higher thanthat of air.

The escape of carbon dioxide into the environment of the lithographicapparatus is reduced by collecting the carbon dioxide, radiallyoutwardly of the gas knife opening 210, through the gas recovery opening61.

In all of the embodiments of FIG. 4, FIG. 6 and FIG. 9, the at least onegas recovery opening 61 is provided in the fluid handling structure 12itself. In an embodiment the at least one gas recovery opening 61 isprovided in a separate component.

An advantage of using CO₂ in the embodiments is that the potentialdanger of providing an explosive vapour or liquid is reduced by thepresence of carbon dioxide.

In an embodiment an immersion system for an immersion lithographicapparatus is provided. The immersion system comprises a fluid handlingstructure 12 of any of the above embodiments and a gas supply systemconfigured to supply gas to the gas supply opening 220 and the gas knifeopening 210. The gas supplied by the gas supply system is carbondioxide.

In an embodiment, the gas supply system comprises a gas source 211 toprovide gas to the at least one gas knife opening 210 and the at leastone gas supply opening 220. In an embodiment, the same gas source 211 isused to provide gas to the at least one gas knife opening 210 and the atleast one gas supply opening 220, as depicted in FIG. 10. In anembodiment, the gas supplied to the gas supply opening 220 may becontrolled using a valve 217, as depicted in FIG. 11, to redirect gasfrom the gas knife opening 210 to the gas supply opening 220. Using avalve 217 to control the gas supply to the gas supply opening 220 meansthat the flow rate and/or gas velocity of the gas being emitted from thegas supply opening 220 and the gas knife opening 210 may be more easilycontrolled, e.g. the flow rate and/or gas velocity of the gas emittedfrom the gas knife opening 210 and the gas supply opening 220 may be setto selected predetermined values or altered to selected values. Thevalve 217 is depicted as part of the fluid handling structure 12,however, the valve 217 may be outside the fluid handling structure 12.For example, the valve 217 may be connected to or integral with, the gassource 211 or the humidifier 212.

In an embodiment, the gas supply system comprises multiple gas sources.In an embodiment, a first gas source 211 a is used to provide gas to theat least one gas knife opening 210 and a second gas source 211 b is usedto provide gas to the at least one gas supply opening 220, as depictedin FIG. 12. Using different gas sources to supply gas to the gas knifeopening 210 and the gas supply opening 220 means that the flow rateand/or gas velocity of the gas being emitted from the gas supply opening220 and the gas knife opening 210 may be more easily controlled. In anembodiment, the gas supply system comprises multiple gas sources and athird path 218 between a first path 214 and a second path 215 toredirect gas to or from the gas knife opening 210 from or to the gassupply opening 220 respectively. The amount of gas being redirected maybe dynamically controlled using a valve 219, as depicted in FIG. 12. Thegas supply opening 220 and the gas knife opening 210 depicted in FIGS.10, 11, 12 and 13 may be used in any of the embodiments, for example, incombination with, and radially outward of, a meniscus controllingfeature of any of the above embodiments.

In an embodiment, gas is supplied to the gas knife opening 210 from thegas source 211 via the first path 214. In an embodiment, gas is suppliedto the gas supply opening 220 from the gas source 211 via the secondpath 215. In an embodiment, the first path 214 and the second path 215may be joined together on one path between the gas source 211 and thegas knife opening 210 and the gas supply opening 220, for example, asdepicted in FIG. 10. In this embodiment, the first flow speed and thesecond flow speed may be more or less the same. The first flow speed andthe second flow speed may be altered relative to each other. This may bedone in several ways, for example, by providing different shaped flowpaths and/or having different surface areas for the gas knife opening210 and the gas supply opening 220.

The gas knife opening 210 and the gas supply opening 220 are separate.This means that even if they are supplied by the same gas source 211,the flow rate and/or gas velocity of gas exiting each of the gas knifeopening 210 and the gas supply opening 220 can be controlled. Therefore,the flow of gas from the gas knife opening 210 and the gas supplyopening 220 can be optimized.

In an embodiment, the gas supply system comprises a humidifier 212 tocontrol the humidity of the gas provided by at least one of the gassources. In an embodiment, the gas is substantially pure CO₂ gas and ishumidified CO₂ gas. In an embodiment, the humidifier 212 increases thehumidity of the CO₂ gas provided by at least one of the gas sources. Inan embodiment, a humidifier 212 is connected to a gas source 211 asdepicted in FIG. 1 and FIG. 10. In an embodiment, the gas supply systemcomprises multiple humidifiers. In an embodiment, a humidifier may beconnected to each gas source, for example, as depicted in FIG. 11. FIG.11 shows a first humidifier 212 a connected to a first gas source 211 aand a second humidifier 212 b connected to a second gas source 211 b. Inan embodiment, the humidifier 212 may be part of the fluid handlingstructure 12. In an embodiment, the humidifier 212 may not be includedin the immersion system of the gas supply system, i.e. the humidifier212 is not essential.

In an embodiment, the fluid handling structure 12 may comprise areservoir 213. The reservoir may be between the at least one gas supplysystem and the gas knife opening 210 and the gas supply opening 220. Inan embodiment, the reservoir 213 may be a section between the gas supplysystem and at least one of the gas knife opening 210 and the gas supplyopening 220 which has an increased cross-sectional area. In anembodiment, the fluid handling structure 12 may comprise the first path214 from the reservoir 213 to the gas knife opening 210 and the secondpath 215 from the reservoir 213 to the gas supply opening 220. In anembodiment, the reservoir 213 may not be provided, i.e. the reservoir213 is not essential.

Providing a reservoir 213 allows greater control of the gas beingomitted from the gas knife opening 210 and/or the gas supply opening220. For example, the gas may build up in the reservoir 213 and may bemore uniformly distributed from the gas knife opening 210 and the gassupply opening 220 in plan view, for example as depicted in FIG. 4.Providing a humidifier 212 allows greater control of the gas beingomitted from the gas knife opening 210 and/or the gas supply opening220. For example, the humidity of the gas being supplied to the gasknife opening 210 and/or the gas supply opening 220 can be controlled toaffect the humidity of the gas atmosphere adjacent to the meniscus 320.

In an embodiment, the second path 215 between the gas source 211 and theat least one gas supply opening 220 may comprise a flow restrictorsection to reduce the flow rate and/or gas velocity of gas being omittedfrom the gas supply opening 220. The flow restrictor section may be abend and/or reduction in the flow-through area in the second path 215.An example of a bend in the second path 215 is depicted in FIG. 10. Aschematic example of a reduction in flow-through area 216 is depicted inFIG. 11. The flow velocities can be altered and tuned to optimize thegas flow through each of the gas knife opening 210 and the gas supplyopening 220. The flow velocities can be controlled by selecting thecross-sectional areas of the first path 214 and the second path 215 andproviding reductions in the cross-sectional area of the second path 215.As such, the ratio of gas passing through the first path 214 and thesecond path 215 can be controlled.

The surface area of the openings can be selected to help control thespeed at which the gas (e.g. CO₂) exits from the openings. If the gasknife opening 210 and the gas supply opening 220 are supplied with gas(e.g. CO₂) from the same gas source, then having a smaller surface areafor the gas knife opening 210 than the gas supply opening 220 can beused to increase the speed of the gas exiting the gas knife opening 210compared to the speed of the gas exiting the gas supply opening 220. Thesurface areas of the openings can be selected in addition, or as analternative, to restricting the second path 215, as a way of controllingthe speed of the gas exiting the first path 214 and the second path 215.It is not essential that the overall area of the gas knife opening 210is smaller than the overall area of the gas supply opening 220, and theareas may be similar or the same, or the area of the gas knife opening210 may be larger than the gas supply opening 220.

Although providing a gas knife opening 210 and a gas supply opening 220in any of the above embodiments can have advantages such as reducing thenumber of bubbles entering into space 11, the gas knife flow rate maystill result in water marks on the wafer W when above a certainthreshold. Therefore, it may be beneficial to reduce the gas knife flowrate and/or gas knife velocity to try to avoid water marks. This can bedone by modulating the gas knife flow rate when the fluid handlingstructure 12 is in use.

In an embodiment, the amount of gas supplied to the gas supply opening220 and/or the gas knife opening 210 is variable. In an embodiment, thegas supplied to the gas supply opening 220 and/or the gas knife opening210 is dynamically controlled, i.e. the gas supplied can be controlledand varied during use. For example, the gas emitted from either the gassupply opening 220 and/or the gas knife opening 210 may be dynamicallycontrolled depending on certain characteristics of the fluid handlingstructure 12, including but not limited to, the direction of movement,the speed, the velocity, and/or the location of the fluid handlingstructure 12.

In an embodiment, the gas knife opening 210 comprises a series ofdiscrete apertures. For example, the gas knife opening 210 may beprovided with two discrete apertures, for example each aperture beingtwo sides of the shape formed by the gas knife opening 210 shown inFIGS. 5 and 6. Alternatively, the gas knife opening 210 may have asingle discrete aperture along each side of the shape formed by the gasknife opening 210 shown in FIGS. 5 and 6. Thus, the gas knife opening210 may be provided by four discrete apertures. The shape of eachaperture is not particularly limited and the gas knife opening 210 maybe provided by any number of discrete apertures.

Each aperture may be individually controlled to vary the gas flow rateand/or gas velocity of the gas exiting the different apertures of thegas knife opening 210. At least one of the apertures may be dynamicallycontrolled depending on certain characteristics of the fluid handlingstructure 12, including but not limited to, the direction of movement,the speed, the velocity, and/or the location of the fluid handlingstructure 12. For example, when in use, apertures of the gas knifeopening 210 on the advancing side of the fluid handling structure 12 maybe controlled to have gas exiting at a lower gas flow rate and/or gasvelocity than the flow rate and/or gas velocity respectively of gasexiting apertures of the gas knife opening 210 on the receding side ofthe fluid handling structure.

Similarly, the gas supply opening 220 may additionally or alternativelycomprise a series of discrete apertures as herein described, which maybe individually controlled as herein described.

In an embodiment, the gas supplied to the gas knife opening 210 may bedynamically controlled such as to reduce the amount of gas beingsupplied to the gas knife opening 210. In an embodiment, the gassupplied to the gas knife opening 210 may be reduced by redirecting someof the gas from the gas knife opening 210 to the gas supply opening 220.In other words, some of the gas is redirected so that instead of passingthrough the first path 214, some of the gas passes through the secondpath 215. The amount of gas passing through the second path 215 may bedynamically controlled to alter the gas flow rate and/or gas velocity ofthe gas exiting the gas knife opening 210.

In an embodiment, a valve may be provided which allows more gas to bedirected to the gas supply opening 220, thus reducing the amount of gasexiting the gas knife opening 210. Alternatively, the valve may bevaried to reduce the amount of gas directed to the gas supply opening220, thus increasing the amount of gas exiting the gas knife opening210. The valve may be variable to allow the amount of gas passingthrough it to be dynamically controlled. The gas passing through thesecond path 215 may be dynamically controlled by using a valve 217 inthe second path 215, as depicted in FIG. 11. The valve 217 may bevariable to allow different amounts of gas to pass through the secondpath 215. In this way, gas can be by-passed from the gas knife opening210 to reduce the gas flow rate and/or gas velocity of the gas exitingthe gas knife opening 210.

In an embodiment, the gas supply reservoir 213 may a device configuredto dynamically control the gas flow rate and/or gas velocity exiting thegas supply opening 220 and/or the gas knife opening 210. For example,the gas supply reservoir 213 may comprise a valve, similar to valve 217,except located in the gas supply reservoir 213.

Although FIG. 11 depicts the gas supply reservoir 213 and a reduction inflow-through area 216, these are both optional features which may or maynot be included as part of the means for controlling gas flow out of thegas knife opening 210 and/or the gas supply opening 220.

In an embodiment, the first gas supply 211 a and/or the second gassupply 211 b, as depicted in FIG. 12 may be controlled to vary the gasflow rate and/or gas velocity exiting the gas knife opening 210 and thegas supply opening 220 respectively. In an embodiment, at least one ofthe first gas supply reservoir 213 a or the second gas supply reservoir213 b may comprise means for dynamically controlling the gas flow rateand/or gas velocity exiting the gas supply opening 220 and/or the gasknife opening 210. In an embodiment, a device configured to control theflow rate and/or gas velocity exiting the gas knife opening 210 and thegas supply opening 220 may be provided along, or as part of, the firstpath 214 or the second path 215 respectively. For example, a valve (suchas depicted in FIG. 11) may be provided to vary the gas flow through thefirst path 214 and/or second path 215 respectively.

In an embodiment, whether or not any one of the first gas supply 211 a,second gas supply 211 b, first gas supply reservoir 213 a or second gassupply reservoir 213 b is dynamically controlled, gas exiting the gasknife opening 210 may be dynamically controlled by re-directing gas flowtowards the gas supply opening. 220 For example, the fluid handlingstructure 12 may comprise a third path 218 between the first path 214and the second path 215, as depicted in FIG. 13. The third path 218 maycomprise a device configured, for example valve 219, to dynamicallycontrol the gas flow from the first path 214 to the second path 215, orvice versa. When the valve 219 is closed, no flow may travel to or fromthe first path 214 from or to the second path 215 respectively. However,the valve 219 may be opened by varying amounts to control gas flow fromthe first path 214 to the second path 215, to re-direct gas from the gasknife opening 210 to the gas supply opening 220. Alternatively, thevalve 219 may be opened by varying amounts to control gas flow from thesecond path 215 to the first path 214, to re-direct gas from the gassupply opening 220 to the gas knife opening 210.

FIG. 13 depicts the third path 218 being located before the first gassupply reservoir 213 a and the second gas supply reservoir 213 b.However, the third path 218 could be located between any point on thefirst path 214 and the second path 215. In an embodiment, the third path218 could be located after the first gas supply reservoir 213 a and thesecond gas supply reservoir 213 b, i.e. on the side of the reservoirsnearer the gas knife opening 210 and the gas supply opening 220respectively. In an embodiment, the third path 218 may be locatedbetween a point before a reservoir on one path and a point after areservoir on the other path. In an embodiment, a fluid handlingstructure 12 could be provided as in FIG. 13 except that only one of thereservoirs is provided, or neither.

The valve in any of the above embodiments, e.g. valve 217 and valve 219,may be any type of valve which allows variable control of gas throughthe respective path and/or reservoir as appropriate. Any of the abovementioned valves may be electronically controlled. Any of the abovementioned valves may comprise an actuator.

In an embodiment the lithographic apparatus comprises an underpressuresource 222 (illustrated in FIG. 1) connectable to the at least one gasrecovery opening

In an embodiment the immersion liquid provided may be acidic or alkali,irrespective of the type of fluid handling structure 12. The idea ofproviding an acidic immersion liquid has previously been described inEuropean patent application publication no. EP 1,482,372, hereinincorporated in its entirety by reference, in connection with reducinginteraction of immersion liquid with top coat. However, this documentdoes not appreciate the possibility of increasing scan speed as a resultof the acidic immersion liquid. In an embodiment, normal (e.g. neutral)immersion liquid may be used and acidic or alkaline immersion liquid maybe provided through a liquid supply opening in the undersurface of thefluid handling structure 12 radially inwardly of the meniscuscontrolling feature. An example of such a liquid supply opening is theopening 180 illustrated in FIG. 4. A similar opening may be present inany of the other embodiments described herein.

In any of the above embodiments, the gas supply opening 220 may be in aradially inward direction of the at least one gas knife opening 210.Thus the gas knife opening 210 may be radially outward of the gas supplyopening 220 and the space 11.

In any of the above embodiments, the fluid handling structure 12 may becontrolled to switch off the gas knife, i.e. to prevent gas exiting fromthe at least one gas knife opening 210. In such an embodiment, otheraspects of the lithographic apparatus may be altered to avoid or reducethe likelihood of a bubble being included in the immersion liquid, forexample, the scan speed may be reduced when the gas knife is turned off.

As will be appreciated, any of the above described features can be usedwith any other feature and it is not only those combinations explicitlydescribed which are covered in this application. The immersion system ofany one of the above embodiments may be used in a device manufacturingmethod or in a lithographic apparatus.

A fluid handling structure 12 may be provided as any one of the fluidhandling structures 12 described above or for use in any of theimmersion systems described above. The fluid handling structure 12 maybe configured to maintain immersion fluid to a region, the fluidhandling structure 12 having, at a boundary of a space 11. The fluidhandling structure 12 may have at least one gas knife opening 210 in aradially outward direction from the space 11 and at least one gas supplyopening 220 in the radially outward direction from the at least one gasknife opening 210 relative to the space 11. The at least one gas supplyopening 220 may comprise a mesh. The mesh may be replaced with a sieve,porous material and/or an array of holes. For example, the array ofholes may be an array of two or three rows of holes. The array of holesmay comprise holes of approximately 10 μm to 60 μm. The gas supplyopening 220 may have a mesh, sieve, porous material and/or array ofholes to make the flow of gas exiting the gas supply opening 220 morelaminar (than if no mesh, sieve, porous material or array of holes isprovided) to avoid, or reduce the likelihood of, gas exiting the gassupply opening 220 from mixing with air.

In an embodiment, there is provided an immersion system comprising afluid handling structure configured to contain immersion fluid to aregion, the fluid handling structure having, at a boundary of a space:at least one gas knife opening in a radially outward direction from thespace; and at least one gas supply opening in the radially outwarddirection from the at least one gas knife opening relative to the space;and the immersion system further comprising a gas supply systemconfigured to supply substantially pure CO₂ gas through the at least onegas knife opening and the at least one gas supply opening so as toprovide an atmosphere of substantially pure CO₂ gas adjacent to, andradially outward of, the space.

In an embodiment, the gas exits the at least one gas knife opening at afirst gas velocity and the gas exits the at least one gas supply openingat a second gas velocity, the first gas velocity being greater than thesecond gas velocity. In an embodiment, the substantially pure CO₂ gas ishumidified CO₂ gas. In an embodiment, the fluid handling structurecomprises a meniscus controlling feature to resist passage of theimmersion fluid in a radially outward direction from the space, themeniscus controlling feature being radially inward of the at least onegas knife opening. In an embodiment, the gas exits the at least one gasknife opening at a first flow speed and the gas exits the at least onegas supply opening at a second flow speed, the first flow speed beinggreater than the second flow speed. In an embodiment, the fluid handlingstructure comprises the gas supply system. In an embodiment, the gassupply system comprises at least one gas source to provide gas to the atleast one gas knife opening and the at least one gas supply opening. Inan embodiment, the gas supply system comprises a first path between afirst gas source and the at least one gas knife opening and a secondpath between a second gas source and the at least one gas supplyopening, wherein the second path comprises a flow restrictor section,and optionally, wherein the flow restrictor section is a bend and/orreduction in a flow-through area in the second path. In an embodiment,the first gas source and the second gas source are the same gas source.In an embodiment, the at least one gas knife opening and the at leastone gas supply opening are on a surface of the fluid handling structurefacing a substrate and/or a substrate table, wherein the at least onegas knife opening is closer to the substrate and/or substrate table thanthe at least one gas supply opening, and/or the at least one gas knifeopening has a smaller surface area on the surface of the fluid handlingstructure than the at least one gas supply opening. In an embodiment,the fluid handling structure is configured to dynamically control theamount of gas supplied to the gas knife opening by redirecting gas tothe gas knife opening from the gas supply opening, or from the gas knifeopening to the gas supply opening.

In an embodiment, there is provided an immersion system comprising afluid handling structure configured to contain immersion fluid to aregion, the fluid handling structure having, at a boundary of a space:at least one gas knife opening in a radially outward direction from thespace; at least one gas supply opening in the radially outward directionfrom the at least one gas knife opening relative to the space; and a gassupply system configured to supply gas through the at least one gasknife opening and the at least one gas supply opening, wherein gas exitsthe at least one gas knife opening at a higher gas velocity than gasexiting the at least one gas supply opening.

In an embodiment, the fluid handling structure comprises a meniscuscontrolling feature to resist passage of the immersion fluid in aradially outward direction from the space, the meniscus controllingfeature being radially inward of the at least one gas knife opening. Inan embodiment, the gas exits the at least one gas knife opening at afirst flow speed and the gas exits the at least one gas supply openingat a second flow speed, the first flow speed being greater than thesecond flow speed. In an embodiment, the fluid handling structurecomprises the gas supply system. In an embodiment, the gas supply systemcomprises at least one gas source to provide gas to the at least one gasknife opening and the at least one gas supply opening. In an embodiment,the gas supply system comprises a first path between a first gas sourceand the at least one gas knife opening and a second path between asecond gas source and the at least one gas supply opening, wherein thesecond path comprises a flow restrictor section, and optionally, whereinthe flow restrictor section is a bend and/or reduction in a flow-througharea in the second path. In an embodiment, the first gas source and thesecond gas source are the same gas source. In an embodiment, the atleast one gas knife opening and the at least one gas supply opening areon a surface of the fluid handling structure facing a substrate and/or asubstrate table, wherein the at least one gas knife opening is closer tothe substrate and/or substrate table than the at least one gas supplyopening, and/or the at least one gas knife opening has a smaller surfacearea on the surface of the fluid handling structure than the at leastone gas supply opening. In an embodiment, the fluid handling structureis configured to dynamically control the amount of gas supplied to thegas knife opening by redirecting gas to the gas knife opening from thegas supply opening, or from the gas knife opening to the gas supplyopening.

In an embodiment, there is provided a device manufacturing methodcomprising projecting a projection beam of radiation via an immersionfluid onto a substrate in a lithographic apparatus comprising animmersion system, wherein the immersion system comprises a fluidhandling structure configured to contain the immersion fluid to aregion, the fluid handling structure having, at a boundary of a space:at least one gas knife opening in a radially outward direction from thespace; and at least one gas supply opening in the radially outwarddirection from the at least one gas knife opening relative to the space;and the method comprising supplying substantially pure CO₂ gas throughthe at least one gas knife opening and the at least one gas supplyopening so as to provide an atmosphere of substantially pure CO₂ gasadjacent to, and radially outward of, the space, or supplying gasthrough the at least one gas knife opening and the at least one gassupply opening, wherein gas exits the at least one gas knife opening ata higher gas velocity than gas exiting the at least one gas supplyopening.

In an embodiment, there is provided a lithographic apparatus comprisingan immersion system comprising a fluid handling structure configured tocontain immersion fluid to a region, the fluid handling structurehaving, at a boundary of a space: at least one gas knife opening in aradially outward direction from the space; and at least one gas supplyopening in the radially outward direction from the at least one gasknife opening relative to the space; and the immersion system furthercomprising a gas supply system configured to supply substantially pureCO₂ gas the at least one gas knife opening and the at least one gassupply opening so as to provide an atmosphere of substantially pure CO₂gas adjacent to, and radially outward of, the space, or a gas supplysystem configured to supply gas through the at least one gas knifeopening and the at least one gas supply opening, wherein gas exits theat least one gas knife opening at a higher gas velocity than gas exitingthe at least one gas supply opening.

In an embodiment, there is provided a fluid handling structureconfigured to contain immersion fluid to a region, the fluid handlingstructure having, at a boundary of a space: at least one gas knifeopening in a radially outward direction from the space; and at least onegas supply opening in the radially outward direction from the at leastone gas knife opening relative to the space, wherein the at least onegas supply opening comprises a mesh, a sieve, porous material and/orarray of holes.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of integrated circuits, itshould be understood that the lithographic apparatus described hereinmay have other applications, such as the manufacture of integratedoptical systems, guidance and detection patterns for magnetic domainmemories, flat-panel displays, liquid-crystal displays (LCDs), thin-filmmagnetic heads, etc. The skilled artisan will appreciate that, in thecontext of such alternative applications, any use of the terms “wafer”or “die” herein may be considered as synonymous with the more generalterms “substrate” or “target portion”, respectively. The substrate Wreferred to herein may be processed, before or after exposure, in forexample a track (a tool that typically applies a layer of resist to asubstrate W and develops the exposed resist), a metrology tool and/or aninspection tool. Where applicable, the disclosure herein may be appliedto such and other substrate processing tools. Further, the substrate Wmay be processed more than once, for example in order to create amulti-layer integrated circuit, so that the term substrate W used hereinmay also refer to a substrate W that already contains multiple processedlayers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm). The term“lens”, where the context allows, may refer to any one or combination ofvarious types of optical components, including refractive and reflectiveoptical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described.

Any controllers described herein may each or in combination be operablewhen the one or more computer programs are read by one or more computerprocessors located within at least one component of the lithographicapparatus. The controllers may each or in combination have any suitableconfiguration for receiving, processing, and sending signals. One ormore processors are configured to communicate with the at least one ofthe controllers. For example, each controller may include one or moreprocessors for executing the computer programs that includemachine-readable instructions for the methods described above. Thecontrollers may include data storage medium for storing such computerprograms, and/or hardware to receive such medium. So the controller(s)may operate according the machine readable instructions of one or morecomputer programs.

One or more embodiments of the invention may be applied to any immersionlithography apparatus. In particular, but not exclusively, those typesmentioned above and whether the immersion liquid is provided in the formof a bath, only on a localized surface area of the substrate W, or isunconfined. In an unconfined arrangement, the immersion liquid may flowover the surface of the substrate W and/or substrate table WT so thatsubstantially the entire uncovered surface of the substrate table WTand/or substrate W is wetted. In such an unconfined immersion system,the liquid supply system may not confine the immersion liquid or it mayprovide a proportion of immersion liquid confinement, but notsubstantially complete confinement of the immersion liquid.

One or more embodiments of the invention may be used in a devicemanufacturing method.

A liquid supply system as contemplated herein should be broadlyconstrued. In certain embodiments, it may be a mechanism or combinationof structures that provides a liquid to a space 11 between theprojection system PS and the substrate W and/or substrate table WT. Itmay comprise a combination of one or more structures, one or more fluidopenings including one or more liquid openings, one or more gas openingsor one or more openings for two phase flow. The openings may each be aninlet into the immersion space 11 (or an outlet from a fluid handlingstructure) or an outlet out of the immersion space 11 (or an inlet intothe fluid handling structure). In an embodiment, a surface of the space11 may be a portion of the substrate W and/or substrate table WT, or asurface of the space 11 may completely cover a surface of the substrateW and/or substrate table WT, or the space 11 may envelop the substrate Wand/or substrate table WT. The liquid supply system may optionallyfurther include one or more elements to control the position, quantity,quality, shape, flow rate or any other features of the liquid.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1. An immersion system comprising a fluid handling structure configuredto contain immersion fluid to a region, the fluid handling structurehaving, at a boundary of a space: at least one gas knife opening in aradially outward direction from the space; and at least one gas supplyopening in the radially outward direction from the at least one gasknife opening relative to the space; and the immersion system furthercomprising a gas supply system configured to supply substantially pureCO₂ gas through the at least one gas knife opening and the at least onegas supply opening so as to provide an atmosphere of substantially pureCO₂ gas adjacent to, and radially outward of, the space.
 2. Theimmersion system of claim 1, wherein the gas exits the at least one gasknife opening at a first gas velocity and the gas exits the at least onegas supply opening at a second gas velocity, the first gas velocitybeing greater than the second gas velocity.
 3. The immersion system ofclaim 1, wherein the substantially pure CO₂ gas is humidified CO₂ gas.4. An immersion system comprising a fluid handling structure configuredto contain immersion fluid to a region, the fluid handling structurehaving, at a boundary of a space: at least one gas knife opening in aradially outward direction from the space; at least one gas supplyopening in the radially outward direction from the at least one gasknife opening relative to the space; and a gas supply system configuredto supply gas through the at least one gas knife opening and the atleast one gas supply opening, wherein gas exits the at least one gasknife opening at a higher gas velocity than gas exiting the at least onegas supply opening.
 5. The immersion system of claim 1, wherein thefluid handling structure comprises a meniscus controlling feature toresist passage of the immersion fluid in a radially outward directionfrom the space, the meniscus controlling feature being radially inwardof the at least one gas knife opening.
 6. The immersion system of claim1, wherein the gas exits the at least one gas knife opening at a firstflow speed and the gas exits the at least one gas supply opening at asecond flow speed, the first flow speed being greater than the secondflow speed.
 7. The immersion system of claim 1, wherein the fluidhandling structure comprises the gas supply system.
 8. The immersionsystem of claim 1, wherein the gas supply system comprises at least onegas source to provide gas to the at least one gas knife opening and theat least one gas supply opening.
 9. The immersion system of claim 8,wherein the gas supply system comprises a first path between a first gassource and the at least one gas knife opening and a second path betweena second gas source and the at least one gas supply opening, wherein thesecond path comprises a flow restrictor section, and optionally, whereinthe flow restrictor section is a bend and/or reduction in a flow-througharea in the second path.
 10. The immersion system of claim 9, whereinthe first gas source and the second gas source are the same gas source.11. The immersion system of claim 1, wherein the at least one gas knifeopening and the at least one gas supply opening are on a surface of thefluid handling structure facing a substrate and/or a substrate table,wherein the at least one gas knife opening is closer to the substrateand/or substrate table than the at least one gas supply opening, and/orthe at least one gas knife opening has a smaller surface area on thesurface of the fluid handling structure than the at least one gas supplyopening.
 12. The immersion system of claim 1, wherein the fluid handlingstructure is configured to dynamically control the amount of gassupplied to the gas knife opening by redirecting gas to the gas knifeopening from the gas supply opening, or from the gas knife opening tothe gas supply opening.
 13. A device manufacturing method comprisingusing the fluid handling structure of claim 1 in a lithographicapparatus.
 14. A lithographic apparatus comprising an immersion systemcomprising the fluid handling structure of claim
 1. 15. A devicemanufacturing method comprising using the fluid handling structure ofclaim 4 in a lithographic apparatus.
 16. A lithographic apparatuscomprising an immersion system comprising the fluid handling structureof claim
 4. 17. A fluid handling structure configured to containimmersion fluid to a region, the fluid handling structure having, at aboundary of a space: at least one gas knife opening in a radiallyoutward direction from the space; and at least one gas supply opening inthe radially outward direction from the at least one gas knife openingrelative to the space, wherein the at least one gas supply openingcomprises a mesh, a sieve, porous material and/or array of holes.